In general, one of the problems preventing occupation of the moon by people from earth is that of providing semi-permanent or permanent structures for the lunar base.
Among the differences between the moon and the earth is the fact that the gravity of the moon is only about one-sixth that of the earth. Moreover, there is an extreme temperature range on the moon. At the surface, temperature ranges from about -190.degree. C. at night to about +140.degree. C. during the day. Moreover, it should be noted that a lunar day is equivalent to about twenty-eight earth days.
The cost of transporting material to the moon is very high, estimated currently at about $4,000 to $5,000 per pound. Therefore, the construction material must be extremely light. However, in this connection, an important point to bear in mind is that there is no atmosphere and therefore no atmospheric pressure on the moon. Nor are there any moisture, bacteria or chemical corrosion. Hence, structures which might be unsuitable on earth can be practical on the moon.
The soil density of the moon is irregular, whether considered vertically or horizontally. On the maria or plain, bedrock may not be encountered within 200 feet below the surface. Moreover, the moon surface is covered with a porous layer of dust. A spread footing or a raft that bears directly on the soil could be a suitable foundation, but conventional rafts and footings made of steel or concrete raise problems in transporting because of their bulk and weight.
Moonquakes occur, although they are less severe than earthquakes.
Among the special hazards that occur on the moon are the bombardment by micro-meteoroids, erosion by the abrasive micro-meteoroids, dust adherence, cosmic radiation from the galaxy on the lunar surface, and also the more important solar radiation. Structures will need protection from these hazards.
Finally, lunar construction must necessarily be accomplished at a minimum elapsed time and with a minimum of labor, in order to reduce the hazards of exposures and the economic cost.